A variety of optical communications modules exist for transmitting and/or receiving optical data signals over optical waveguides (e.g., optical fibers). Optical communications modules include optical receiver modules, optical transmitter modules and optical transceiver modules. Optical receiver modules have one or more receive channels for receiving one or more optical data signals over one or more respective optical waveguides. Optical transmitter modules have one or more transmit channels for transmitting one or more optical data signals over one or more respective optical waveguides. Optical transceiver modules have one or more transmit channels and one or more receive channels for transmitting and receiving respective optical transmit and receive data signals over respective transmit and receive optical waveguides. For each of these different types of optical communications modules, a variety of designs and configurations exist.
In order to meet ever-increasing demands for higher information bandwidth, state-of-the-art digital communication switches, servers, and routers often use multiple rows of optical communications modules arranged in very close proximity to one another to increase module density. To be a commercially fungible product, the optical communications modules generally need to have basic dimensions and mechanical functionality that conform to an industry standard Multi-Source Agreement (MSA). Of course, many optical communications module designs that comply with and add value beyond the basic mechanical functionally set forth in the MSA are possible.
One known optical transceiver module design that complies with such an MSA is the Small Form-Factor Pluggable (SFP) optical communications module. SFP optical communications modules are designed to mate with an opening formed in a cage. The module housing has one or more receptacles configured to mate with one or more respective optical connectors that terminate ends of respective optical fiber cables. The most common type of optical connector used with SFP optical transceiver modules is called the LC optical connector.
When an SFP or similar type of optical transceiver module is in a stored position inside of a cage, catches formed in opposite sides of the module housing engage respective latches formed in opposite sides of the cage to prevent the module housing from inadvertently coming out of the cage opening. The SFP module housing is typically a two-piece part comprising an upper metal housing portion and a lower metal housing portion that are secured to one another. Module housings of this type typically include a pair of cage latch stops formed on opposite outer side walls of the module housing that engage the pair of latches formed on opposite side walls of the cage to secure the module housing to the cage when the module housing is fully inserted into the cage. With these types of module designs, a relatively complex latching/delatching mechanism is mechanically coupled to the module housing and is operable to temporarily deform the latches of the cage to delatch, or disengage, the latches of the cage from the latch stops of the module housing. Once the module housing has been delatched from the cage, the module can be extracted from the cage.
One issue that needs to be addressed when designing optical communications modules is electromagnetic interference (EMI) shielding. In most optical communications modules, the receptacle that receives the optical connector disposed on the end of the optical fiber cable constitutes an EMI open aperture that allows EMI to escape from the module housing. The Federal Communications Commission (FCC) has set standards that limit the amount of electromagnetic radiation that may emanate from unintended sources. For this reason, a variety of techniques and designs are used to shield EMI open apertures in module housings in order to limit the amount of EMI that passes through the apertures. Various metal shielding designs and resins that contain metallic material have been used to cover areas from which EMI may escape from the housings. So far, such techniques and designs have had only limited success, especially with respect to optical communications modules that transmit and/or receive data at very high data rates (e.g., 10 gigabits per second (Gbps) and higher).
For example, EMI collars are often used with pluggable optical communications modules to provide EMI shielding. The EMI collars in use today vary in construction, but generally include a band portion that is secured about the exterior of the module housing and spring fingers having proximal ends that attach to the band portion and distal ends that extend away from the proximal ends. The spring fingers are periodically spaced about the collar and have folds in them near their distal ends that direct the distal ends inwardly toward the module housing. The distal ends make contact with the upper and lower metal housing portions at periodically-spaced points on the housing. At the locations where the folds occur near the distal ends of the spring fingers, the outer surfaces of the spring fingers are in contact with the inner surface of the cage at periodically spaced contact points along the inner surface of the cage. Such EMI collar designs are based on Faraday cage principles.
The amount of EMI that passes through an EMI shielding device increases with the largest dimension of the largest EMI open aperture of the EMI shielding device. Therefore, EMI shielding devices such as EMI collars and other devices are designed to ensure that there is no open aperture that has a dimension that exceeds the maximum allowable EMI open aperture dimension associated with the frequency of interest. For example, in the known EMI collars of the type described above, the spacing between the locations at which the outer surfaces of the spring fingers come into contact with the inner surface of the cage should not exceed one quarter wavelength of the frequency of interest that is being attenuated. Even greater attenuation of the frequency of interest can be achieved by making the maximum EMI open aperture dimension significantly less than one quarter of a wavelength, such as, for example, one eighth or one tenth of a wavelength. However, the ability to decrease this spacing using currently available manufacturing techniques is limited. In addition, as the frequencies of optical communications modules increase, this spacing needs to be made smaller in order to effectively shield EMI, which becomes increasingly difficult or impossible to achieve at very high frequencies.
The metal housing and the latching/delatching mechanism of the known SFP module described above contribute significantly to the cost of the SFP module. The metal housing is needed because it is part of the EMI shielding solution. In addition, the cage consumes a large amount of space in the system, which leads to reduced mounting density and reduced bandwidth. A need exists for a pluggable optical communications module configuration and system that obviate the need for the metal housing and the latching/delatching mechanism, thereby reducing costs, while continuing to provide EMI shielding and pluggability.